Translator for IP Networks, Network System Using the Translator, and IP Network Coupling Method Therefor

1. A method of rendering communications between first and second devices, said first device using Internet Protocol version 6 (IPv6) as a communication protocol, and said second device using Internet Protocol version 4 (IPv4) as a communication protocol, comprising the steps of: receiving from said first device, an IPv6 packet having an IPv6 header; judging whether an IPv4-mapped-IPv6 address is stored in a destination address of said IPv6 header; when said judging step judges that the IPv4-mapped-IPv6 address is stored, extracting lower 32 bits from said IPv4-mapped-IPv6 address to create the extracted lower 32 bits as a translated IPv4 address; translating said IPv6 header into an IPv4 header including said translated IPv4 address as a destination address; creating an IPv4 packet having said translated IPv4 header from said IPv6 packet; and sending said created IPv4 packet to said second device.

2. A method according to claim 1 , further comprising the steps of: holding at least one IPv4 address; assigning to an IPv6 address of said first device included in said IPv6 header as a source address, any of said held at least one IPv4 address; and in the step of translating said IPv6 header, translating said IPv6 header into said IPv4 header including the assigned IPv4 address of said held at least one IPv4 address as the source address.

3. A method according to claim 2 , further comprising the step of: storing said IPv6 address of the first device and the assigned IPv4 address to correlate with each other.

4. A method according to claim 2 , further comprising the step of: sending address translation information, including the IPv6 address of said first device and said any IPv4 address assigned to the IPv6 address of said first device, to said second device.

5. A method according to claim 1 , further comprising the steps of: pre-storing an IPv6 address of said first device and any IPv4 address to correlate with each other; translating IPv6 address of said first device included in said IPv6 header as a source address into said any IPv4 address pre-stored to correlate with the IPv6 address; and in said IPv6 header translating step, translating said IPv6 header into said IPv4 header including said IPv4 address as a source address.

6. A method of rendering communications between first and second devices, said first device using a first class protocol and having an assigned address of a first length, and said second device using said second class protocol and having an assigned address of a second length, said method comprising the steps of: receiving from said first device a first class packet having a first class header and being communicated using a first class protocol; judging whether an address of a format indicating to include an address of said second class protocol is stored in a destination address of said first class header; when said judging step judges that the address of a format indicating to include an address of said second class protocol, extracting said second address from said address of a format indicating to include an address of said second class protocol to create the extracted second address as a translated address of said second class protocol; translating said first class header into a second class header including the translated address of said second class protocol as a destination address and different from said first class header in header format; creating a second class packet having said translated second class header from said first class packet and being communicated using said second class protocol; and sending said created second class packet to said second device.

7. A method according to claim 6 , further comprising the steps of: holding at least one address of the second class protocol; assigning to said first address included in said first class header as a source address, any of said held at least one address of the second class protocol; and in the step of translating said first class header, translating said first class header into second class header including the assigned address of said held at least one address of the second class protocol as the source address.

8. A method according to claim 7 , further comprising the step of: storing said first address and the assigned address of said held at least one address of the second class protocol to correlate with each other.

9. A method according to claim 7 , further comprising the step of: sending address translation information including said first address and said address assigned to said first address, to said second device.

10. A method according to claim 6 , further comprising the steps of: pre-storing said first address and any of addresses of the second class protocol to correlate with each other; translating said first address included in said first class header as a source address into any address pre-stored to correlate said first address; and in said first class header translating step, translating said first class header into said second class header including said any address as a source address.